Soft glass and composite article



R. H. DALTON SOFT GLASS AND COMPOSITE ARTICLE original Filed March 4,V 194e June 23, 1953 l 2 Sheets-Sheet l INVENTOR. $055297 A( u ro/y June 23, 1953 R. H. DALToN SOFT GLASS AND COMPOSITE ARTICLE v Original Filed March 4, 1946 2 Sheets-Shea?I 2 INVENToR. /90 effe r A( /u ro/v rroR/rfy Patented June 23, 1953 UNITED STATES PATENT OFFICE SOFT GLASS AND COMPOSITE ARTICLE Robert H. Dalton, Corning, N. YY., assignor to YCorning Glass Works, Corning, N. Y., a corporation of New York Original application March 4, 1946, Serial No. 651,818. Divided and this application February 1, 1950, Serial No. 141,831

and entitled Soft Glass and Composite Article.

The joining together of glass parts by interfusion thereof requires a practically perfect match in expansion coefcients of the glass parts to be joined and a careful control of local temperatures in and near the joint. A high degree of manual skill or complex machinery is also essential despite which distortion of the glass parts adjacent to the joint invariably occurs.

The primary object of this invention is to provide a fusion weld between glass parts` at lower temperature than has heretofore been possible and without distorting the. parts at or adjacent to the weld.

Another object is to provide glass compositions for forming such welds.

Another object is to provide glasses having unusually low softening temperatures together with expansion coeflicients suitable for uniting sodalirne-silica glasses and other glasses of similar expansion characteristics. y

Another object is to provide a method for sealing together glass parts lof considerable size or complicated shapes whereby the glass parts are uniformly heated throughout and are not subjected vto thermal shock.

Another object is to provide a method for sealing together glass parts which does not'require high degree of manual skill nor the use of complicated sealing machinery. v f

A further object is to provide fabricated glass articles comprising `preformed glass parts joined by a fusion weld of another glass having a lower softening temperature than the glass parts.l

Another object isto seal a glass partition within a hollow Aglass body, such as a glass cell or tube. Y l f The softening temperatureof a glass vas referred to herein is that'temperature at which a thread of the glass, .65 to l rmm. in diameter and 23 cmrlong, willr elongate atf the rate of 1 mm. per minute when heated throughout the upper 9 cm. of its length. VSee A method for measuring the softening temperature 'of glasses, by J. T. Littleton, Journal` of. the American Ceramic Society, vol. 10, page 259 (1927).

In order to form a fusion weldbetween two glass parts without distortion thereof, a small amount of another glass may be 'employed as a brazing or soldering glass which has such aY tening temperature of the glass parts. I have found that for best results the softening tem; perature of the soft brazingglass shouldy be not higher than the annealing temperature of the glass to be joined therewith and preferably should be 200 C. or more below the softening temperature of the latter. Annealing temperature is that temperature at which'` all strainin the glass is released in about fteen (15) minutes. See A method for determining the annealing temperature of glass, by Littleton and Roberts, Journal of the American Optical So'- ciety, vol. 4, page 224 (1920).

The softlbrazing glass will, of course,'diifer in' composition from the glass parts to be joined, Ingredients which are most effective in lowering thesoftening temperature ofA glass comprise -the alkali metal oxides, boric oxide, lead oxide, etc.` The amount of the alkali metal oxides which may be employed for this purpose is limited bythe desiredV expansion coeicient of the glass because the alkali metal oxides increase the .expansion coefficient more than any other material. Lead oxide also causesa substantial increase inthe expansion coeflicient. All such ingredients, when used in very substantial amounts tend tolower the chemical durability of the glassl or its re"-` sistance to attackby water andjchemical rea-v gents. Materials, such as aluminajwhich in' crease the chemical durability of glass generally` have -a hardening effect andtend to raise its expansion coefficient as v wellV as its softeningy temperature. v v

I have found that in glasses which consist esi sentially of PbO, B203 andv S102, and in which the PbO exceeds the substitution of A1203 lfor SiO'z unexpectedlynlowers theeXpansion co4 eiicient of the glass (and in some cases also its softening temperature) and at thesametime improves its chemical durability and resistance to devitrication. This is unusual, "because it is well known that SiOz' is very eective in lowerklng the expansion coefficient of glassv and rebe compensated by the addition of more PbO.

low softening temperature that it will nieltand flow at temperatures considerably below the sof- Since .PbO -tends to l soften` the glass `while raising itsexpansion c"oeflicient,...thevr netresult is that replacement orSiQz-,bylzosandrbo permits softening v`the *glassl without substantially changing'its expansion coefficient. j" Q,j' f j By Vsuch means I have beenv able-tof-produce glasses which 'have eXpansio'n'coeI-iicients- 'bee meeirni 1o-7 and 90 1o-7 per c.x o`to 300 C.) and which have softeningtemperatures 'bei low 500 C. and as low as 430 C. .'I'hese new borhood of 700 C. or highenand .the annealing temperatures are above 5009 Q, The expansion coeicients to 300 C.) o f such glasses range from about 80 l07 to 100 10JI per C., this range being particularly suitable for forming seals using the new soft glasse s, as will later appear. The new glasses have chemical d-urability and resistance to devitriiication adequate for the purpose hereinbefore set forth.

The new glasses on the-*oxide basis comprise at least three components consisting. of PDQ', A1203. and one .or both of the class-forming oxides B203 and .SiOa- The term elassdormheoxides as-used herein, refers to thoseoxides which have the property of forming glasses .of and by them,- selves when cooled. ironia molten condition. Aof cording to the book Eroperties oi ..Glass, by G W.. Morey, .the outstanding glasseiormng oxides are B293, S103 .and-P295, .but P205. is not suitable in the. present glasses.

The new glasses may contain 60%, to 8.5% PbO, 5% .to 15% A1203, 0%.to 40% B203, and .0% to SiOz. Preferably, .the proportions should be 70% 110.80% PbO,f5% to .1.5% A1203, 5% to 20% B203, and .0% to` 10% S102, becauseV the latte;` proportions produce glasses which lhave softening temperatures less than 5.0.0.o C. and expansion coefficients between 75; .1.0." `and 9.0 10' per C., .and which .are particularly suitablefor joining commercial soda-lime-,and other glasses ofVV similar expansion characteristics.,

Preferably, the newglasses consist .of the fou-1 components PbO, A1203, B203, v and Si02 in the proportions stated abolie, but minor amounts of other constituents mayfalso be presentsubiect to the following considerations. The amount of such .minor constituents. preferably should not exceed about..2% to .5%v butk in .someinstanoes may amount. toasmuchfas 8%` .or 10% of the total glass composition. T Ihe .alkali noetal oxides,

if present, should not exceed about 1%., because theycausea decidedincrease in .the expansion coeicient of the glass without advantageous .gain in softness. Other minor. constituents may -i-nclude .oxides of the metals .of Ythe-second periodic with an adhesive .dipped into the .powdered group vand bismuth oxide. Fluorine. aids somewhat in lowering the softening temperature o f the glass but .also tends .to cause..dev itrieation and to .lower its chemical durablityfizf -verysmuoh of itis present. It .ma-y be introduced as `lead iluoride, .aluminum iinoride or alkali metal .fluoride. 'The following compositions which-are ex.- pressefd in terms of vweight percentage'as calcu-A lated from their batches .generally villustrate glasses which are within the scope of the invention.

L20 Scitening Tommi()A Exp. coefE. per "CX101 V71% PbO.

.sevenY times theme03.

V'4 Composition 1 is particularly suitable for my purpose .In .Composition spart of` the lead is introduced as PbgFc, butA on.. the oxide basis the total percentage of lead in this glass is about In the new glasses the percentage of PbO should not be more than about 17 times the Apercentage 'of .A1203 and it will be noted that in the .above examples it does not exceed The high alumina content with .respect .to PbO is a distinguishing characteristic of the present glasses and is higher Vthan was heretofore believed desirable for soft .glasses and. glazes, of high lead content, As pointed out above, the presence of a relatively high .alumina content in the present glasses is largely responsible for their unusually low softening. temperatures.. the .other desirable voye desoiihedspit glasses may los ap-l o o .elassports ih The plico to theiuhot. various. ways for parts with .a permanent.. tortion of .the Parli? melted and. .llowedl 'Westmont disbly., the selft glass is a s all .stream oh to vone o the shriaoes to .loe joined. the glass, part heine heated atleast sufficiently-to prevent breakeee .trom thermal shoeh .This is advantageously accomplished while theglass part is still hot from molding or pressing. Tliehot surface to be coated may alternatively be dipped into the soft glass, the latter being either molten or pulverized. In the latter caseV the Ypowderedsoft glass becomes sticky and .adherent from the .hoot of the gloss part. lhin rods s tr ips, or washers of the soft gloss .may 'be inserted. between 'the ports to be joined and subsequently heated in v mace ora rod of the soft glass -may be rubbed or smeared 01.1 t9 .the hot surfen@ to be joined. Other methods of applying the soft glass vto the joints of the glass. parts may include .applying it either as o .molten liquid es e slurry Comprising o powder ip .e Vehicle soph .cellulose .nitrato so111- tion by .flow-lhs., brushing; or Spraying, or by means vof a coating roller.v TheV powdered soft glass may he attache, .1h appropriate patterns to paper or other suitable backing material hy i: means ofY en adhesive aholtherssftsr .they be op" plied `to the surface to be .costei Preformod.

soft glass to obtain a oating'jthereof.

coated with thesoft glass arebrooeht together and heated suiciently to cause the vsoft glass to flow and ll thejolht: hilt .ihfshlllplohtlytosoiten the .glass parts themselves Heating .is preferably .accomplished by posshs the, article through a lehr or oven, whereby the composite article when finished is also annealed. However, it may 5" alsgjbe accomplished through the application o f local 'heat sufficient for the p urposeby the use .of a name, orhy elettrici-.inductive heating, or, in the ease .of thin articles. hy the. application thereto .of .o hot ,metallic 'hody .ih the peiehborhood ofthe seal.

The amount ,Of the soft glass which is res quired toiill thejoint is `relatively small and will depend .upon the Character of the surfaces to be 'iohod- With .surfaces which .are .formed so as to nt closely and accurately .a .very thin layer of vthe soft. slasssuinoes to ,melee .a .satisaotory -seoL Wthless closely'tting joints, @larger amount @f the soft glass .is .required the Vamount in any 1 case being suflicient to fill all irregularities vof the junction. When the parts nt closely and the layer of the soft glass is very thin, the average values of the expansion coeiiicien't'of the softk .glass between room temperature and the setting point temperature and the expansioncoeiiicient of' the glass parts (0 to 300 C.) need not match as closely as when the 'layer of the soft glass is relatively thick. In the former instance it suffices if the expansion coeicient of. the soft glass (averaged as above) is within about 20 ror 30x10-7 per C. of that of the glass parts. The setting point temperature is the temperature below which the glass has insuiiicient'plastic ow.

to relieve strains set up in the glass during cooling. For most glasses this temperature is ap# proximately to 20"'Cbelowtl'ieir annealing temperatures. I have found that the'expansion coefficients (0 to 300 C.) "or" the soft glass should preferably be about 2 to `l5 10I per C; below that of the glass parts to be joined.` This is because a strain-free seal' between two glasses of diiferent softening temperatures requires that the overall thermal elongation per unit length' between room temperature and the setting point temperature of the softer Aglass should be the same for both glasses. Under these conditions. the expansion coeiicients (0 to 300 C.) of

6 lar to that shown in Fig. 9 before Welding the parts together according to the invention.

Fig. 12 is a transverse sectional View o f a double bore ,glassv tube during fabrication in accordance with the invention; and f Fig. 13 is a transverse' sectional viewY of a^nished double bore tube'similar to` that shown in Fig. 12.

Fig. 1 unisi-,rates one method of applying the' soit welding glass to the edgeof a glass part to be welded to another glass part, for example,"

the glass parts of anfall glass automobile head lamp known as a sealedbeam headlamp. A. small electric furnace generally designated i0, comprising a platinum' liner Il surrounded by a. ceramic refractory shell sistance element l'and an outer insulating refractory shell I4, is mounted on a 'swinging support I5. The furnace!!! containsiamoltensupf the new soft glasses are about 2 to 15 l0-" per C. less than that of commercial soda-lime silica vglass'and other glasses of similar expansion characteristics. In general, .the soda-lime silica glasses which can be joined by meansefthe vnew soft glasses comprisev the approximate range of compositions including 70%-76% SiOi,l l3%-18% alkali metal oxides (R20), 844% CaOel-MgO and 1%-3% A1203. Other glasses of similar expansion characteristics such as lead glasses, barium crown glasses, etc., mayl also be used. Y Y w For a better understanding oi thevsuse and application of the new soft glasses to. preform parts of sodi-lime glasses for welding them to-y gether and of Various glass articles madethereby,

reference is had to the accompanying `drawings in which: i Fig. l is an. elevation partly in section of anv apparatus for producing glass articles provided with a sealing strip of soft glass in accordance with the invention.

Fig. 2 is an elevation partly in section of a lamp comprising two glass parts joined by a fusionv weld of soft glass in accordance with the inven tion. s

Fig. 3 is an elevation partly in section of a cathode ray tube embodying the invention.

Fig. 4 is a planv view of a double Window pane.

made in accordance with. thev invention.

Fig. 5 is a fragmentary section on an enlarged scale on the line 5 5 of Fig. 4.

Fig. 6 isa fragmentary section ontan yenlarged scale of a double window pane during` welding in accordance with the invention. Fig. '7 is a sectional view of a hollow glass build ing block weldedin accordance with the invention. u

Fig. 8 is a sectional View of a sheet of foam glass faced with a transparent glass sheet welded thereto in accordance with the invention.

Fig. 9 is aplan view partly broken away( of av hollow glass panel for a fluorescent lamp in vaccordance with the invention. s

Fig. l0 isa sectional `View on the lineV l-IIJ of Fig. 9. Y

Fig. 11 is a sectional view ofa glass panel simi-Y ply of soft glass IE, preferably the composition ,1 described above, which issues as afcontinuous stream I'I from an orifice I8 in the bottom of' the furnace I.- The stream"il falls` within a groove I9 provided in the rim of a lens or cover glass 20 for a sealed beam headlampwhich is' therewith of a tongue onthe rim of the re-v fiector part of the headlamp (not shown) when the reflector is subsequently welded to the lens 20. rlhus the invention may .provide asfan article of manufacture a glass part provided with an integralstrip of a soft brazing glass vready for the subsequent Ajoining thereto of .another glass part by'fusion of the parts.`

' Fig. 2 illustrates sealed beam type which comprises a lens 24 similar to the lens 20 of Fig. 1 andfusion welded to a glass' reflector 25 by a thin layer 2t of soft glass, the reiiector being provided with a lilanient 2 land electrodes 28.` s s s In Fig. 3 is shown a cathode ray tube co1n. prising an accurately shaped face 29 joined to `a conica1 body 30 by an integral layerjl oi soft glass.

In Figs. 4 and g5,v a

face of the sheet32jat its borderand upstandfling Yrib of glass 35 .with which the sheet'isis In this case junction o f the sheets provided. 32 and 33 may be accomplished as 4shown in Fig. 6 wherein a rod of .soft glass is disposed on an upstanding rib 3'Iof a glass. sheet 88 and another sheet of glass 39 isdisposed on the glass rod 36. Welding maybe yaccomplished by' pass-V ing the assembled sheets of gla'ssthrough a lehr having a maximum temperaturer above the soifA tening temperature of the'soft glass but below the deformation temperature of the glass sheets. Such a seal would be difficult or impossible to make by conventional name sealing methods.

In Fig. '7y the two halves ofoJ hollow'glass building block 40 'are'joined by layer 4| of a s'oftglass I2, an electric re'- welding withoutA distortion `ailnished headlamp of the flatsheet or glass. iis. permanently joined to another sheet 3,3. icy-'means of a layer 34 of soft glass disposedbetween the,

T' disposed between; the edges? oiv their: rimsf and integral therewith..

Irl-.Eiga 8 a'.sheetfof"foamzgla'ssfllZ isxjoined by one-.face to alii'atsheet of-gl'ass 43, suchzas window glass by an intermediateflayerfdd of a soft gla'sslwhich .is integral therewith;

InFigs. 9 and 10, a'glasszpanelgenerally ignated 45, comprises identical upper and lower halves which are provided: with'rims Miand' projecting. ribsV 41, theA rims and ribsV of the two halves being inaccurate registration. Theftwo" halves are joined by'layers l48 of softzglass dis.- p'osed between the abutting rimszdxandi ribs 41 a'nd integrally unitedA therewith'. Junction of the two halves maybe: accomplished'. as shown in Fig. 11 wherein strips Miei; soft glass are disposedbetween the respective rims EDan-d ribs I. of twoglass parts similar. to the.v two halves of` the. panelof Fig. 10. Thefopposing rims 50 and ribs. 5|l of 'the' two' glass', parts are brought. intov contact with vthe respective' intermediate stripsv 49. and the entire? assembly is heated 'tof atemperature sufficient to soften the strips 49 butA insuicient to soften the twoV glass parts after. which the;V assembly is annealed.

The glasspanelV described in. Figs. 9 and 10 isadapted to be convertedinto a panel type fluorescent lamp by applying.Y to. all interior surfaces a coating of iluorescent material and providing two inserted electrodes. (not shown), the electricdischarge being constrained by the intervening ribs to traverse the'V longestl possible path between the electrodes and. consequently to uniformly illuminate theV entire panel.

In- Fig. V12 a glass tube 5.2. is. provided with a longitudinally disposed upstanding glass partition. 53. Rods 500i soit glass are longitudinally positioned along the lower edge of the partition 53l in which condition, the assembly is. heated suffciently to soften the. rods. 5 and cause the soft glassv to low and make a uniformjoint between thewall of the tube 52. andv theedge of the partition53. In a similar manner soft glass rodsmay be applied and fused into place. at the opposite edge of. thel partition 53 whereupon a double bore tube is produced similar to that illustrated. in-Fig. 13 inwhich a glass tube 55 is provided with a glass partition. 56 joined thereto through an integral joint 51 of soit glass.

The invention possesses. numerous benefits and advantages, outstanding among which is the ability to form junctions of hard. glasses at temperatures below their strain temperatures, the latter temperature being., definedV as that temperature at which four hours is required to anneal the glass (Littleton and Roberts, Jour.' Am. 0pt. Soc., vol. 4, p. 224. (1920) above referred to). Thatris to say, glasses having, .expansion coefcients. within the range specified above and having strain temperatures vabove the softening temperature of the soft brazng Vglass of the invention canV be joined by means of said soft brazing glass without introducing permanent strain in the composite article and hence avoiding the necessity for annealing the article after the joint is complete. Since hard glasses` of high expansion can be strengthened by tempering or chilling to purposelyl introduce permanent uniform stresses in the glass,` the new soft glasses ofv the invention can be employed toV join such. tempered glass parts without releasing the stresses. Y y

The new soft soldering glasses also may be advantageously used in the production ofV glass-tometal seals in which a glass part having anv eX- agceagcss pansioh: coecient'` in therange 80 `10l to l00 10r1 per. C2 (05 to 300 C.) is joined to a metal partV having' a similar expansion coefcientby anf intermediateY layer of the new soft solderingy glass; Y

{I claim: 'i

1'. A transparentglass which comprises 70% to 80%'. PbO, 5% to 20%' B203, and 5% to 15%'Y A1202, the sumV of PbO, B203, and A1203 being over 90%. Y

2. A. transparentl glass. which comprises '70% to;8'0% PbO, 5%; to 20% B203, 5%' to 15% A1203, and not' over 10%- Si02, the sum of PbO, B203, A1203 S102Y being over-90%. y

3; Atransparentzglass'. composition which consists of 70%; to.80.% PbO, 5% to 20% B203, 5% toiV 15%1Al203, and notiover- 10%' Si02.

4. transparentglass-.composition whichl consistsof approximately '75% PbO, 11% B203, 11% A1203', and 3% $102.1

5;V A. composite article comprising at least two parts composed of: Yglass comprising 'l0-76% VSi02, 13-18.% R20, 84.2%' CaO and` MgO and 1-3%,` A1203, and. ai layer" ofi another glass between the parts? and integral therewithY which comprises. '70% to 8.0%, PbO, 5%, to 20% B202, 5%to 15 A1203v and not over 10% Si02, thesum ofv PbO, 13203,. A1203 andi S102, being over 90%.

6. Acomposite article comprising at least two parts composeo'lv of; glass Vhaving an expansion coeicient (0 to 30.0 0.-) trom aboutA 80 10-l toy 100 107 per C ..and av layer. or another glass between the. parts and integralv therewithY consisting of approximately 75% P bO,v 11% B203; 11% 111203 and 3%; S102'.`

7. A. hollow doublewalledV glass article comprising two sheets of sodajlime glass, the face of one sheet. being opposed to theiace of the other. sheet and. spaced therefrom by a plurality of ribs of the same glass which form a part of at least.V one ofi the sheets, the twov sheets being joined and, hermetically sealed by means oia layer of4 soft glass consisting of approximately 75%y PbO,z 11%.. B203', 11%, A1203 and 3% S102 between and. integralA with contacting parts of;

` the sheets, the expansion coeiiicient of the soda to 15' 10'I per C. higher rthan that of the soft glass between 0 and 300 C.

9. A composite article comprising at least, two

parts composed oi glassl having an expansionV coecent (0 to 300 C.) from about 80 l07 to 100 10r per C..,. and a layer of another glass between. the parts: and integral therewith, comprising 70% toV 80%- Pb0, 5% to 20% B203, and 5% to 15% A1203, the sum of PbO, B203 and A1203 being over 10. A composite article comprising at least two parts composed. of glass having an expansion coefficient (0 to 300 C.) from about 80 107 to tor 107 per C.,y and a layer of another glass between the parts and, integral therewith comprising '10% to 80% PbO, 5% to 20%Y B203, 5% to 15% A1203, and not over 10% S-i02, the sum, of PbO, B202, A1203 andv S102 being over 90%.

11. A hollow double-walled glass article comprising two sheets o-f soda lime glass, the face of one sheet beflng opposed toI the face of the other sheet and spaced therefrom by a plurality of ribs of the same glass which form a part of at least one of the sheets, the two sheets being joined and hermetically sealed by means of a layer of soft glass comprising '70% to 80% PbO, 5% to 20% B203, and 5% to 15% A1203, the sum` of PbO, B203 and A1203 being over 90%, between and integral with contacting parts of the sheets, the expansion coefcient of the soda lime glass being up tol 15 10'7 per C. higher than that of the soft glass between and 300 C.

12. A double window pane comprising two sheets of soda lime glass, the faces of which are in opposed relationship and are spaced from each other by a plurality of upstanding glass ribs which form a part of one sheet and are joined to the second sheet by an integral layer o-f soft glass comprising 70% to 80% PbO, 5% to 20% B203, and to 15% A1203, the sum of PbO, B203 and A1203 being over 90%, the expansion coelcient of the soda llime glass being up to 15 107 per C., higher than that of the soft glass between 0 and 300 C.

13. A composite article comprising at least two parts composed of glass comprising 70-76% Si02, 13-18% R20, 8-14% CaO and MgO and 1-3% A1203, and. a layer of another glass between the parts and integral therewith which comprises '70% to 80% PbO, 5% to 20% B203, and 5% to 15% A1203, the sum of PbO, B203, and A1203 being over 90%.

14. A hollow double-walled glass article comprising two sheets of soda lime glass, the face of one sheet being opposed to the face of the other sheet and spaced therefrom by a plurality of ribs of the same glass which form a part of at least one of the sheets, the two sheets being joined and hermetically sealed by means of a layer of soft glass comprising '70% to2 80% PbO, 5% to 20% B203, 5% to 15% A1203, and not over S102, the sum of PbO, B203, A1203 and S02 being over 90%, between and integral with contacting parts of the sheets, the expansion coeiicient of the soda lime glass being up to 10JI per C. higher than that of the soft glass between 0 and 300 C.

15. A double window pane comprising two sheets of soda lime glass, the faces of which are in opposed relationship and are spaced from each other by a plurality of upstanding glass ribs which forma part of one sheet and are joined to the second sheet by an integral layer of soft glass comprising r% to 80% PbO, 5% to 20% B203, 5% to 15% A1203, and not over 10% Si02, the sum of PbO, B203, A1203 and Si02 being over 90%, the expansion coefficient of the soda lime glass being up to 15 107 per C., higher than that of the soft glass between 0 and 300 C.

16. A composite article comprising a glass part having a` thermal expansion coeicient in the range x10-7 to 100 10rl per C. between 0 and 300 Ci, a metal part having a thermal expansion coeiiicient compatible with that of the glass, and a glass sealing the metal part to the glass part and comprising 70% to 80% PbO, 5% to 20% B203 and 5% to 15% A1203, the sum of PbO, B203 and A1203 being over 90%.

17. A composite article comprising a glass part having a thermal expansion coeilicient in the range 80x10-V7 to 100 107 per C. between 0 and 300 C., a metal part having a thermal eX- pansion coefficient compatible with that of the Y glass, and a glass sealing the metal part to the glass part and comprising 70% to 80% PbO, 5% toi-20% B203, 5% to 15% A1203 and not over 10 Si02, the sum of PbO, B203, A1203 and Si02 being over 90%.

18. A transparent glass which comprises '70% to PbO, 5% to 20% B203, and 5% to 15% A1203, the sum of PbO, B203 and A1203 being over 19. A transparent glass which comprises 70% to 85% PbO, 5% to 20% B203, 5% to 15% A1203, and not over 10% Si02, the sum of PbO, B203, A1203 and Si02 being over 90%.

20. A transparent glass composition which consists of 70% to 85% PbO, 5% to 20% B203, 5% to 15% A1203, and not over 10% Si02.

ROBERT H. DALTON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date y 1,793,039 Yetter Feb. 17, 1931 2,032,003 Clause Feb. 25, 1936 OTHER REFERENCES Eitel-Pirani-Scheel: Glastechnische Tabellen (1932), page 708. 

4. A TRANSPARENT GLASS COMPOSITION WHICH CONSISTS A APPROXIMATELY 75% PHO, 11% B2O3, 11% AL2O3, AND 3% SIO2.
 8. A DOUBLE WINDOW PANE COMPRISING TWO SHEETS OF SODA LIME GLASS, THE FACES OF WHICH ARE IN OPPOSED RELATIONSHIP AND ARE SPACED FROM EACH OTHER BY A PLURALITY OF UPSTANDING GLASS RIBS WHICH FORM A PART OF ONE SHEET AND ARE JOINED TO THE SECOND SHEET BY A INTEGRAL LAYER OF SOFT GLASS CONSISTING OF APPROXIMATELY 75% PHO, 11% B2O3, 11% AL2O3 AND 3% SIO2, THE EXPANSION COEFFICIENT OF THE SODA LIME GLASS BEING UP TO 15X10-7 PER *C. HIGHER THAN THAT OF THE SOFT GLASS BETWEEN O* AND 300* C. 